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Molecules 2014, 19(4), 4418-4432; doi:10.3390/molecules19044418

Synthesis of Regiospecifically Fluorinated Conjugated Dienamides

, ,  and *
Department of Chemistry, The City College and The City University of New York, 160 Convent Avenue, NY 10031, USA
* Author to whom correspondence should be addressed.
Received: 16 February 2014 / Revised: 22 March 2014 / Accepted: 31 March 2014 / Published: 10 April 2014
(This article belongs to the Special Issue Fluorine Chemistry 2016)
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Modular synthesis of regiospecifically fluorinated 2,4-diene Weinreb amides, with defined stereochemistry at both double bonds, was achieved via two sequential Julia-Kocienski olefinations. In the first step, a Z-a-fluorovinyl Weinreb amide unit with a benzothiazolylsulfanyl substituent at the allylic position was assembled. This was achieved via condensation of two primary building blocks, namely 2-(benzo[d]thiazol-2-ylsulfonyl)-2-fluoro-N-methoxy-N-methylacetamide (a Julia-Kocienski olefination reagent) and 2-(benzo[d]thiazol-2-ylthio)acetaldehyde (a bifunctional building block). This condensation was highly Z-selective and proceeded in a good 76% yield. Oxidation of benzothiazolylsulfanyl moiety furnished a second-generation Julia-Kocienski olefination reagent, which was used for the introduction of the second olefinic linkage via DBU-mediated condensations with aldehydes, to give (2Z,4E/Z)-dienamides in 50%–74% yield. Although olefinations were 4Z-selective, (2Z,4E/Z)-2-fluoro-2,4-dienamides could be readily isomerized to the corresponding 5-substituted (2Z,4E)-2-fluoro-N-methoxy-N-methylpenta-2,4-dienamides in the presence of catalytic iodine.
Keywords: fluoro dienamides; Julia-Kocienski olefination; Weinreb amide; fluoro dienes fluoro dienamides; Julia-Kocienski olefination; Weinreb amide; fluoro dienes
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Chowdhury, M.; Mandal, S.K.; Banerjee, S.; Zajc, B. Synthesis of Regiospecifically Fluorinated Conjugated Dienamides. Molecules 2014, 19, 4418-4432.

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